In most process plants with piping in which fluids are transported, a number of valves are used so that the liquid flow can be controlled, stopped and/or conducted from one pipe system to another.
The valves include a valve housing in which valve body, valve seats etc. are mounted. The valve housing is typically made by a machining process as this is a well-known and tested manufacturing process. However, there are drawbacks in using the machining process as it e.g. requires application of large and complicated machines, e.g. CNC-machines, cutting or machining, starting with a piece of work and proceeding to the finished valve housing. Furthermore, there is a great waste of material in machining operations, as the cuttings are not recyclable and thus treated as waste material.
In the food industry, it is very important that fittings, e.g. pipe transitions, valves, pipe connections and similar used in the process plants, fulfill strict quality requirements. They are to be equipped with special internal even and cleaning-friendly surfaces, as edges, projections, holes and the like otherwise may constitute a possible contamination trap and thus impede good hygiene. This also applies to valve housings, which are to have smooth inner surfaces so that liquid residues cannot be accumulated and thereby constitute a trap for residues and impede cleaning of the pipe system.
The drawbacks in connection with machining processes may be avoided by using cold-working processes. Cold-working processes are advantageous in that they provide the finished article with smooth transitions without edges or rough faces that may trap fluid residues and which are also cleaning-friendly. Besides, cold-working may provide dimensionally accurate details, something which is not so easy with articles worked at high temperatures. Furthermore, cold-working is possible with the stainless steel alloys most often used in the food industry. Finally, the cold-working process does not leave much, if any, waste material.
Such cold-working methods for the valve housings and other components for pipe systems are known. A circular blank is formed into a pot with largely rotational/symmetrical shape, the pot is provided with a number of openings in its side and/or end faces, and at least one of the openings is drawn into a pipe branch by forcing a ball from an inner cavity in the component and outwards. In the process, material from the central parts of the components are drawn out into the wall of the pipe branch, the process thus distributing material from central regions to peripheral parts of the component.
An example of such a method is known from U.S. Pat. No. 4,083,219 where a drift forces the ball down through a cut opening opposite an already made pipe stub. The component in question is supported by a saddle-shaped female die. The internal parts of the die are rounded so that the material around the opening through which the bore is forced assumes an outer shape corresponding to the rounded details of the die. However, this method only provides a very short pipe stub around the opening, and further molding and extending of the pipe stub is difficult or impossible as the material around the deformation zone will be distorted, and since there is no control of the deformations, there is a risk of unacceptable dimensional changes, excessive thinning of the wall material, or even breaking of the material of the component.